Shore Power/grounding/bonding/transformers ????

[MikeP]

Dove the boat yesterday - zincs were nearly gone in only 2+ months (we won't even talk about the barnacles and my 10.5K top speed two days prior). So I'm doing some research re galvanic corrosion.

The Hatt manual, in relation to the "Shoreline Transformers" that came with our 1980 53 MY boat states: "This yacht is equipped with shoreline isolation transformers." Further it states, "Additionally, the shoreline ground wire need not be connected to the yacht's bonding system and, thus, educes the possibility of galvanic corrosion from stray shore currents."

Obviously, there is a lot of galvanic corrosion going on.

Does the info in the Hatt manual mean that the ground wire of the 240 50A shore power cord does not have to be connected to the boat and it could be "lifted" and possibly reduce galvanic corrosion? Based on the manual it sounds optional BUT I don't know if the reference to connection to the yacht's bonding system means the actual neutral wire from shore or it means some internal boat connection between the neutral and bonding system.

Any thoughts?

 

[Boatsb]

Was it having the same problem at the previous marina? How do you know it's coming from your boat?

 

[MikeP]

No, it didn't happen at our previous marina - 6months+ was normal. As I understand stray current, my zincs can be eaten by currents from other boats or shore power leakage. I'm told that one boat on our dock has (or had) significant leakage that rapidly ate up zincs of all boats around them.

If some sort of wiring change can reduce that - and it appears that Hatt specifically considers that - then I'm going to make whatever wiring change, if any, that can improve it.

 

[Jim saco]

Mike I'm sorry for your troubles.
I don't believe that lifting the ground of your xformer would be safe or eliminate any problem with your zincs. The isolation xformer should always have a common equipment ground which would make it common to everything else on the boat. The isolation is there so that you always have clean and even voltage on your boat no matter the input. I can't explain your zinc loss. I've had similar problems on my boat also. I think that if you remove the ground something could become energized if there was a fault somewhere internally. The input and the output of the xformer don't know each other because there is no electrical connection between the two, however the core of the xformer is common. I know all this nonsense doesnt solve your problem but, I don't want you to put yourself in a dangerous position.

 

[spcoolin]

Hatteras is not saying remove shore ground...

What they are saying is with isolation transformers installed, there should be no shore ground connection to zinc...

Think 2 separate grounds...Shore is one....

The bonding system is the other that connects all metal to zinc...
Which would cover DC grounds connected to each engine thru the water & zinc.

Steve~

 

[MikeP]

Ah.. gotcha!

So I guess I need to determine if there currently is a connection between shore ground and bonding and, if so, eliminate it.

 

[daniel r morrison]

A galvanic isolator could be installed in series with the green earth ground on your incomming shore power. This should stop small stray current flow but afford a solid path for short circuits keeping the system safe. With an isolation transformer you have no physical connection between the primary and secondary windings thus your ground path back to the ground on shore is broken. Most of the time there is a bonding jumper between the neutral tap on the secondary and the grounding terminal on the boat. This is necessary to provide short circuit protection that will trip breakers or blow fuses rather than leave exposed metal parts energized. I have seen some systems, not in boats, that don't have this bonding jumper as they power equipment located where volitle vapors are present that the sometimes spark with a system short could ignite. These systems usually have a ground fault indicator that lets you know a short circuit exists.
Check the boats around you to be sure no one has an automotive battery charger in use, this can certainly do what you have described.

 

[davidwigler]

Nigel Calder's book explains the isolation transformers and speaks highly of them for reducing galvanic corrosion.

Two large isolation transformers are mounted on the port side of the generator room. I also have a galvanic isolator mounted on the inside of the starboard hull in the starboard engine room. Strange, I would think the transformers and isolator would be located near each other. Something tells me the isolator is not OEM. I have no idea how or if the transformers and isolator are wired together, or whether one isolator can protect two shorepower lines.

You might want to get some expert advice on adding a galvanic isolator.

 

[SeaEric]

It is my understanding that much of the stray current issues at Piney Narrows come from the land line phone wires on the dock and their voltage involved in dial tone. Does anyone on that dock still have an active land line phone? I think the marina should consider pulling that wiring out. Of course, the AC supply wires all go underwater at high tide adjacent to slip G-1. That can't help either.

 

[jim rosenthal]

Stray current issues which case galvanic corrosion are usually DC, not AC. The phone company, I think, DOES use DC in its land line circuits. I would be surprised if anyone at PNYH still has an land line phone on their boat- it might very well be a good idea to turn off those circuits. Shouldn't take more than an act of Congress, knowing the phone company.

 

[SeaEric]

Shouldn't take more than an act of Congress, knowing the phone company.

Not so at this point. A few years ago Verizon gave up on the dock wiring at PNYH and (I think) gave it to us. All they provide now is dial tone. Now days if you want a land line phone the PNYH staff installs it.

 

[rsmith]

Phone lines today are 36v more than enough to give you a tingle and cause electrolisis if their in the water. I've never gotten more than 3-4 months out of the zinks. I have heard that salinity has a lot to do with the ability of stray currents to roam around looking for zinks to eat. Then again there are always "problem boats". There are no large boats within 500'of me but ocasionaly my neighbors son inlaw would bring his old 33 Concorde over when his father inlaw went north. I dive my boat once a month and in 3 weeks when the Concorde was there my zinks were gone. After 2 months and 2 sets of zinks I went over and talked to him. Seems he put a Discount auto inverter on the boat and for what ever reason every piece of metal in the boat was hot. If you stood in the shower and touched the handles you got buzzed. Not a full jolt but somewhere between shuffling your feet across a wool carpet and sticking your finger in a light socket. naturaly he knew it all and couldnt be his problem. Strange thing every time he left the boat the plug got pulled out. He finaly gave up and sold the boat.(his wife had issues with the getting shocked part)

 

[davidwigler]

"Two large isolation transformers are mounted on the port side of the generator room. I also have a galvanic isolator mounted on the inside of the starboard hull in the starboard engine room. Strange, I would think the transformers and isolator would be located near each other. Something tells me the isolator is not OEM. I have no idea how or if the transformers and isolator are wired together, or whether one isolator can protect two shorepower lines."


Out of curiosity I studied this issue and resolved some mysteries about Windsong. The original starboard Shorepower 1 50 amp/125 shorepower receptacle (the middle input of the three) was replaced with a 50 amp 120/240 input, and it was disconnected from the isolation transformers. Instead, it goes to a large ship/shore power selector and uses the galvanic isolator both in the starboard ER where the 5 compressors are. So, if hooked to shorepower on the starboard side only, one can use a dedicated 50 amp 120/240 circuit for the airconditioners only and still have Shorepower 1 for everything else. 24,000 watts. Pretty cool until the power bill arrives.

 

[Bugsy]

A long-standing member of this forum worked with me extensively on researching this whole "zinc loss" issue and though I had barely an inkling of his explanations (and even less memory), I believe he indicated that you do NOT use an isolation transformer with a galvanic isolator. Hence, I have a galvanic isolator in my dock box.

He had an instrument for the measurement of DC voltage in the surrounding water and variations depending upon the area tested were significant.

I was at Miami Beach Marina for a few years. The tidal current there is fairly strong. I exhausted zincs quite quickly. I moved to Crandon Park Marina on Key Biscayne where there was negligible current and my zincs lasted almost three times as long.

In short, there are a LOT of factors that affect zinc loss but my first suspicion would always be an adjacent or nearby boat.